The invention relates to a blend of lube base oils which provides improved oxidation stability, both with additives and without additives.
Finished lubricants used for automobiles, diesel engines, and industrial applications consist of two general components: a lube base oil and additives. In general, a few lube base oils are used to generate a wide variety of finished lubricants by varying the mixtures of individual lube base oils and individual additives. This requires that lube base oils be stored without additives prior to use. Also, lube base oils are an item of commerce and are bought, sold and exchanged. Since the receiver of the lube base oil wants to formulate specific finished lubes, they do not want to receive lube base oils that already contain additives. Thus, lube base oils in almost all circumstances do not contain additives, and are simply hydrocarbons prepared from petroleum or other sources. Thus one general requirement for a lube base oil is that it have good stability during shipment and storage in the absence of additives. In addition, it is desirable that the finished lubricant have as good a stability as possible. In this case, the stability is the resistance to oxidation and formation of deposits during shipment and storage in the presence of additives and other compounds that simulate use in commercial equipment. The preferred lube base oil is one that has a combination of good stability without additives and with additives.
Thus, there is a need in the art for a lube base oil that has good stability both with and without additives. There is further a need in the art for a way to make this improved lube base oil from supplies of lube base oil that are generally deficient in at least one measure of stability. Moreover, there is a need in the art for such a lube base oil that can provide good stabilities without the need for special additives. This invention provides such a lube base oil.
The present invention is directed to lube base oils with improved stability against oxidation. In particular, the lube base oil product of one embodiment of the invention is a blend of a synthetic lube base oil and a non-synthetic lube base oil wherein the lube base oil product has a greater stability in the absence of additives than the stability of the synthetic lube base oil and has a greater stability in the presence of additives than the non-synthetic lube base oil.
A lube base oil according to the invention comprises at least one synthetic lube base oil having an iso-paraffin content greater than 50%; and at least one percent of a non-synthetic lube base oil selected from the groups consisting of Group I lube base oils, Group II lube base oils with a sulfur content greater than about 50 ppm, petroleum-derived Group V lube base oils, or mixtures thereof. Preferably, the synthetic lube base oil will have an Oxidator A value in the absence of additives less than about 1 and the non-synthetic lube base oil will have an Oxidator A value in the absence of additives greater than about 5. In one embodiment of the invention, the synthetic lube base oil is obtained from a Fischer Tropsch process.
In another embodiment of the invention, a lube base oil is provided comprising at least one synthetic lube base oil having a sulfur content less than about 50 ppm and at least one percent of a non-synthetic lube base oil having a sulfur content greater than about 300 ppm and selected from the groups consisting of Group I lube base oils, petroleum-derived Group V lube base oils, or mixtures thereof. Preferably, the synthetic lube base oil will have an Oxidator A value less than about 1 and the non-synthetic lube base oil will have an Oxidator A value greater than about 5.
In another embodiment of the invention, a lube base oil is provided comprising at least one synthetic lube base oil having an Oxidator A value in the absence of additives of less than about 1 and an Oxidator BN value in the presence of additives greater than about 7; and a non-synthetic lube base oil having an Oxidator A value in the absence of additives greater than about 5 and an Oxidator BN value in the presence of additives less than about 10.